The present invention relates to detection of light and pertains particularly to a color sensor circuit with integrated programmable gain selection.
A typical color sensor circuit detects three colors. The three colors are typically red, blue and green. Three separate components are used to implement each color of a color sensor. A first component includes a photodiode and filter that are used to detect an illuminance for the color. The second component is an operational amplifier that functions as a transimpedance amplifier. The third component is a feedback resistor. Typically, the three components for each color are mounted on a printed circuit board (PCB).
Typically, the photodiodes have a relatively large area which is necessary to generate high photocurrents. The high photocurrents are necessary to make the sensor circuit less susceptible to noise. Correspondingly large values for feedback resistors are also used. The values of external resistors are selected to give the proper gain needed for the transimpedance amplifier.
The required feedback resistance and feedback capacitance vary from system to system, which has made it necessary in the prior art to implement the feedback resistor on a separate component from the photodiodes.